feat(turbopack): externalType support global (#80542)
This pr introduces a new external type for turbopack(maybe not for
next.js), it can help to generate external like:
https://webpack.js.org/configuration/externals/#externalstypeglobal.
- Support a new externalType `global`
- Update the codengen content for `external_module.rs`
---------
Co-authored-by: Benjamin Woodruff <benjamin.woodruff@vercel.com>
